Method of inhibiting corrosion using a composition of quaternary ammonium salts containing non-halogen anions

ABSTRACT

Disclosed are quaternary ammonium carbonates, bicarbonates, and mixtures thereof as anti-corrosive agents. The invention relates to a method for inhibiting the corrosion of metal surfaces by applying a composition containing one or more quaternary ammonium carbonate or bicarbonate. The disclosure is also directed to anti-corrosive coating for metal substrates containing these compounds, to metal substrates having these anticorrosive coatings, and to aqueous cleaning solutions containing these compounds.

CROSS REFERENCE OF PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/021,511, filed Sep. 9, 2013, which claims the benefit of U.S. patentapplication Ser. No. 11/299,301, filed Dec. 9, 2005, which claims thebenefit of U.S. Provisional Application Ser. No. 60/634,794, filed Dec.9, 2004, and is a continuation-in-part of U.S. patent application Ser.No. 10/857,636, filed May 28, 2004, which is a continuation-in-part ofU.S. patent application Ser. No. 10/810,279 filed Mar. 26, 2004, whichclaims the benefit of U.S. Provisional Application Ser. No. 60/474,081filed May 28, 2003, all of which are incorporated by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates to the use of quaternary ammonium saltscontaining non-halogen anions (e.g., quaternary ammonium carbonates andbicarbonates) as anticorrosive agents.

BACKGROUND

In processes where metal surfaces come in contact with water, whether asliquid water or humid air, there is always the danger of corrosion. Thisis particularly problematic when the metal itself is prone to corrosionand is not coated.

Examples of metals prone to corrosion are found in stamped metal carparts made from ferrous alloys, abraded surfaces such as machined steelparts, and machine components made from cast iron. Although corrosioninhibitors (or anticorrosive agents) have been known for many years,most are still inadequate. One key inadequacy is that of watersolubility. Most corrosion inhibitors are produced from long chain fattyacids and derivatives and often have poor aqueous solubility. This isespecially problematic when the metal surface contacts both water andoil, such as in oil and gas production, petroleum processing, and metalworking applications. Petrochemical processing itself presents a widearray of challenges for corrosion inhibitors including cooling systems,refinery units, pipelines, steam generators, and oil or gas producingunits.

In order to reduce the rate of corrosion of metals (such as metalvessels, equipment metal parts, equipment surfaces, pipelines, andequipment used to store the fluids), especially those containing iron,corrosion inhibitors are typically added to the fluid contacting themetal. The fluid may be a gas, a slurry, or a liquid.

Traditional solvents for cleaning metal and metal parts, such as mineralspirits and kerosene, have been replaced in recent years by aqueousformulations due to concerns about volatile organic carbons (VOCs). Thismove toward water-based formulations for cleaning metal parts is notwithout problems. Water does not solubilize grease or oily residueseasily, and water itself can markedly increase the corrosion of themetal parts themselves. In addition, formulations are typically used asmicroemulsions, which require the use of additional surfactants forstabilization during the cleaning process. Morpholine is frequently usedin these cleaning formulations to provide corrosion protection. However,morpholine does little to contribute to cleaning, and does not stabilizethe microemulsion, since it is not a good surfactant. Furthermore,morpholine is a regulated product, since it may be used to prepareillicit drugs.

Quaternary ammonium compounds have found limited use as corrosioninhibitors. U.S. Pat. No. 6,521,028 discloses the use of particularpyridinium and quinolinium salts, in either propylene glycol orpropylene glycol ether solvents, as corrosion inhibitors.

U.S. Pat. Nos. 6,080,789, and 6,297,285 disclose the use of quaternaryammonium carbonates as disinfectants.

U.S. Pat. No. 4,792,417 discloses a composition for inhibiting stresscorrosion of stainless steel in contact with aqueous and/or polarorganic solutions which contain chloride ions and optionally cuprousions. The composition comprises an aqueous or polar organic solution ofa particular quaternary ammonium alkylcarbonate or quaternary ammoniumbenzylcarbonate.

There is still a need for corrosion inhibitors that possess goodaffinity for metallic surfaces and are both water and oil soluble.Additionally, there is a desire for new corrosion inhibitors that addcleaning and or surfactant capability. Corrosion inhibitors that alsoafford antimicrobial protection to the finished formulation to whichthey are applied would be particularly advantageous.

DESCRIPTION OF THE INVENTION

It has now been discovered that quaternary ammonium salts containingnon-halogen anions (such as quaternary ammonium carbonates andbicarbonates) inhibit the corrosion of metals.

Here and hereinbelow, non-halogen anions are any anions other thanhalide anions such as fluoride, chloride, bromide and iodide, anionsderived from oxo acids of halogens such as chloric or perchloric acidand anions containing halogen bound to other nonmetallic or metallicatoms, such as tetrafluoroborate, hexafluorophosphate,tetrachloroferrate and the like.

The present invention relates to a method for inhibiting the corrosionof metal surfaces by applying (or depositing) a corrosion inhibitingeffective amount of a composition comprising (a) at least one quaternaryammonium salt containing a non-halogen anion, and (b) optionally, asolvent. This method is particularly useful for down-hole applicationsin oilfields and metal working.

According to one preferred embodiment, the composition comprises (a) atleast one quaternary ammonium carbonate, bicarbonate, or a mixturethereof; and (b) optionally, a solvent.

Another embodiment is an anti-corrosive coating for metal substrates.The coating includes at least one quaternary ammonium salt containing anon-halogen anion, and a coating material. Typically, the quaternaryammonium salt containing a non-halogen anion is dispersed in the coatingmaterial. According to a preferred embodiment, the coating also exhibitsantimicrobial efficacy. The coating may include an antimicrobialeffective amount of the anti-corrosive quaternary ammonium saltcontaining a non-halogen anion or of a different antimicrobial agent.

According to one preferred embodiment, the coating includes at least onequaternary ammonium carbonate, bicarbonate, or a mixture thereof, and acoating material.

Yet another embodiment is a metal substrate having the anticorrosivecoating of the present invention on a surface thereof.

Yet another embodiment is the use of an aqueous solution comprising acorrosion inhibiting effective amount of at least one quaternaryammonium salt containing a non-halogen anion as an anti-corrosivecleaning solution. The aqueous cleaning solution may be an aqueous-basedmetal cleaner.

According to one preferred embodiment, the aqueous solution comprises acorrosion inhibiting effective amount of at least one quaternaryammonium carbonate, bicarbonate, or a mixture thereof as ananti-corrosive cleaning solution.

Yet another embodiment is the use of an aqueous or non-aqueous solutioncomprising a corrosion inhibiting effective amount of at least onequaternary ammonium salt containing a non-halogen anion as ananti-corrosive metalworking fluid. According to one preferredembodiment, the aqueous or non-aqueous solution comprises a corrosioninhibiting effective amount of at least one quaternary ammoniumcarbonate, bicarbonate, or a mixture thereof as an anti-corrosivemetalworking fluid.

Yet another embodiment is the use of an aqueous or non-aqueous solutioncomprising a corrosion inhibiting effective amount of at least onequaternary ammonium salt containing a non-halogen anion as a corrosioninhibitor in powder metallurgy. According to one preferred embodiment,the aqueous or non-aqueous solution comprises a corrosion inhibitingeffective amount of at least one quaternary ammonium carbonate,bicarbonate, or a mixture thereof as a corrosion inhibitor in powdermetallurgy.

Corrosion Inhibitor Compositions

The present invention is directed towards the inhibition of corrosion ofmetal substrates. The term “inhibition of corrosion” as used hereinincludes, but is not limited to, the prevention or reduction in the rateof oxidation of a metal surface, generally when the metal is exposed towater or air, or a combination of the two. The oxidation of metal is anelectrochemical reaction generally resulting either in a loss of metalfrom the surface or an accumulation of oxidation products at the surfaceof the metal. The term “metal” as used herein includes, but is notlimited to, steel, cast iron, aluminum, metal alloys, and combinationsthereof. In one embodiment, the metal substrate is an aerosol can.

According to the invention, the corrosion of a metal substrate isinhibited by a method comprising the step of contacting the substratewith a composition comprising

-   -   (a) at least one quaternary ammonium salt containing a        non-halogen anion, and    -   (b) optionally, a solvent.

Quaternary ammonium salts useful in the present invention include, butare not limited to, those having the formula:

wherein R¹ is an optionally aryl-substituted C₁₋₂₀ alkyl group, and R²is an optionally aryl-substituted C₁₋₂₀ alkyl group, R³ and R⁴independently of each other are C₁₋₄ alkyl groups, X^(n−) is an anionselected from the group consisting of hydroxide, carbonate, bicarbonate,phosphates, phosphites, hypophosphite, nitrate, sulfates, borates,anions of saturated and unsaturated acyclic C₁₋₂₀ monocarboxylic acids,anions of saturated and unsaturated C₂₋₂₀ dicarboxylic acids, and anionsof hydroxy-substituted carboxylic acids, and n denotes the appropriatenumber of negative charges of said anion.

According to one embodiment, the quaternary ammonium salt(s) have theformula above with the proviso that, if both R³ and R⁴ are methyl,X^(n−) is neither carbonate nor bicarbonate.

Here and hereinbelow, C₁₋₂₀ alkyl groups are linear or branched alkylgroups having 1 to 20 carbon atoms, including, but not limited to,methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl,tert-butyl, pentyl, isopentyl, hexyl, heptyl, octyl, nonyl, isononyl,decyl, dodecyl, tetradecyl, hexadecyl, octadecyl and icosyl.Aryl-substituted C₁₋₂₀ alkyl groups are any of the above groups bearingan aryl group, in particular phenyl, as a substituent. Preferredexamples of aryl-substituted C₁₋₂₀ alkyl groups are benzyl, phenylethyland phenylpropyl.

The term “phosphates” is to be understood as including both acid andneutral salts of phosphoric acid, namely, dihydrogenphosphates (H₂PO₄⁻), monohydrogenphosphates (HPO₄ ²⁻) and phosphates (PO₄ ³⁻), as well assalts of oligo- and polyphosphoric acids such as diphosphates(pyrophosphates) and triphosphates.

Phosphites are salts of phosphorous acid containing the anions H₂PO₃ ⁻and/or HPO₃ ²⁻.

Sulfates are hydrogensulfate (HSO₄ ⁻) and sulfate (SO₄ ²⁻) as well asdisulfate (S₂O₇ ²⁻) and related anions.

Borates are any anions derived from boric acid (H₃BO₃) and the variouspolyboric acids.

Saturated and unsaturated acyclic C₁₋₂₀ monocarboxylic acids are inparticular alkanoic acids, such as formic, acetic, propionic, butyric,pentanoic, hecanoic, octanoic, decanoic, dodecanoic, tetradecanoic,hexadecanoic, octadecanoic and icosanoic acids, or alkenoic acids, suchas acrylic, methacrylic, oleic and linolic acid.

Saturated and unsaturated acyclic C₂₋₂₀ dicarboxylic acids are inparticular alkanedioic acids, such as oxalic, malonic, succinic,glutaric and adipic acid, or alkenedioic acids such as fumaric or maleicacid.

Hydroxy-substituted carboxylic acids are any carboxylic acids bearing atleast one hydroxy group in addition to the carboxylate group(s), such asglycolic, malic, citric or salicylic acid.

According to one embodiment, R¹ and R² are C₄₋₂₀ alkyl oraryl-substituted C₄₋₂₀ alkyl groups.

According to a preferred embodiment, R¹ is a C₈₋₁₂ alkyl oraryl-substituted C₈₋₁₂ alkyl group.

The aforementioned quaternary ammonium salts can be prepared by methodsknown in the art, for example by anion-exchange reactions usingcommercially available quaternary ammonium salts as starting materials.

Preferably, R³ and R⁴ in the quaternary ammonium salts containing anon-halogen anion are methyl groups.

In a preferred embodiment, R¹ and R² in the quaternary ammonium salts(I) denote the same C₁₋₂₀ alkyl group.

In a more preferred embodiment, R¹ and R² in the quaternary ammoniumsalts (I) denote C₁₀ alkyl groups, most preferably n-C₁₀ alkyl groups.

In another preferred embodiment, R¹ in the quaternary ammonium salts (I)denotes a methyl group. More preferably, both R¹ and R² denote a methylgroup.

In still another preferred embodiment, R¹ in the quaternary ammoniumsalts (I) denotes a benzyl or phenylethyl group.

The above described quaternary ammonium salts can be used alone ascorrosion inhibitors or formulated into corrosion inhibitorformulations.

Unlike traditional quaternary ammonium chlorides, the quaternaryammonium salts containing non-halogen anions described herein not onlyhave low corrosion properties, but act as corrosion inhibitors.

The salts are easily soluble in or even miscible with water, have highoil solubility, and have a high affinity for metal surfaces. Inaddition, they increase the solubility of oils, such as fragrance oilsand lipophilic substances, in aqueous solutions.

Other quaternary ammonium carbonates useful in the present inventioninclude, but are not limited to, those having the formula:

wherein R⁵ and R⁶ are each independently a C₁₋₂₀ alkyl group or anaryl-substituted C₁₋₂₀ alkyl group (e.g., a benzyl group). R⁵ and R⁶ maybe the same or different.

The term “aryl-substituted alkyl group” refers to an alkyl groupsubstituted by one or more aromatic carbon rings, in particular phenylrings, such as phenylethyl (the alkyl group being bound to the nitrogenatom) or benzyl.

The term “C_(n-m) alkyl group” (for example, “C₁₋₂₀ alkyl group”) refersto any linear or branched alkyl group having from n to m (for example,from 1 to 20) carbon atoms.

According to one embodiment, R⁵ and R⁶ are C₄₋₂₀ alkyl oraryl-substituted C₄₋₂₀ alkyl groups.

According to a preferred embodiment, R⁵ is a C₈₋₁₂ alkyl oraryl-substituted C₈₋₁₂ alkyl group.

A more preferred quaternary ammonium carbonate isdidecyldimethylammonium carbonate, such as di-n-decyldimethylammoniumcarbonate.

Didecyldimethylammonium carbonate is available as a 50 percent by weightsolution in water containing 4 percent or less by weight of an alcohol,such as methanol or ethanol.

The solution is a yellow/orange liquid that has a slightly fruity odor.

Suitable quaternary ammonium bicarbonates include, but are not limitedto, those having the formula:

wherein R⁵ and R⁶ have the meanings and preferred meanings as definedabove for the quarternary ammonium carbonates (II).

A preferred quaternary ammonium bicarbonate is didecyldimethylammoniumbicarbonate, such as di-n-decyldimethylammonium bicarbonate.

The aforementioned quaternary ammonium carbonates and bicarbonates canbe prepared by methods known in the art, such as those described in U.S.Pat. No. 5,438,034 and International Publication No. WO 03/006419.

The quaternary ammonium carbonates and bicarbonates are in equilibrium.The concentrations of bicarbonates and carbonates vary depending on thepH of the solution in which they are contained.

In a preferred embodiment, R⁵ and R⁶ in the quaternary ammoniumcarbonates (II) and/or bicarbonates (III) denote the same C₁₋₂₀ alkylgroup.

In a more preferred embodiment, R⁵ and R⁶ in the quaternary ammoniumcarbonates (II) and/or bicarbonates (III) denote C₁₀ alkyl groups, mostpreferably n-C₁₀ alkyl groups.

In another preferred embodiment, R⁵ in the quaternary ammoniumcarbonates (II) and/or bicarbonates (III) denotes a methyl group. Morepreferably, both R⁵ and R⁶ denote a methyl group.

In still another preferred embodiment, R⁵ in the quaternary ammoniumcarbonates (II) and/or bicarbonates (III) denotes a benzyl orphenylethyl group.

The above described quaternary ammonium carbonates and bicarbonates canbe used alone as corrosion inhibitors or formulated into corrosioninhibitor formulations.

Unlike traditional quaternary ammonium chlorides, the carbonate andbicarbonate based quaternary ammonium compounds described herein notonly have low corrosion properties, but act as corrosion inhibitors.

The carbonates and bicarbonates are miscible in water in allconcentrations, have high oil solubility, and have a high affinity formetal surfaces. In addition, the carbonates and bicarbonates increasethe solubility of oils, such as fragrance oils and lipophilicsubstances, in aqueous solutions.

Suitable solvents for the quaternary ammonium salts containingnon-halogen anions include polar solvents (such as water andwater-miscible polar solvents), glycols, glycol ethers (such aspropylene glycol) and mixtures thereof.

Optionally, one or more additional surfactants may be included in thecomposition. Suitable surfactants include non-ionic surfactants,cationic surfactants (other than the quaternary ammonium saltscontaining non-halogen anions described herein), anionic surfactants,amphoteric surfactants, and mixtures thereof. Non-limiting examples ofsuch surfactants are amine oxides, linear alcohol ethoxylates, secondaryalcohol ethoxylates, ethoxylate ethers, betaines, fatty acids containingfrom 6 to 22 carbon atoms, salts of said fatty acids, and mixturesthereof. For example, the surfactant may be nonylphenol ethoxylate.

The quaternary ammonium corrosion inhibitors inhibit corrosion of metalsin aqueous and oil environments, including water and oil mixtures (e.g.,in down-hole applications in oilfields and metal working). Anon-limiting example of an oil found in an oil environment is apetroleum distillate. Examples of petroleum distillates include, but arenot limited to, kerosene, white spirits, and hydrocarbon fractions. Inmetal working, aqueous solutions and water-oil mixtures or emulsions arefrequently used for lubrication (such as for lubricating metal workingtools).

Other conventional additives, such as builders, colorants, perfumes,fragrances, cleaners, and mixtures thereof, may be included in theanticorrosive composition.

The amount of quaternary ammonium salts containing non-halogen anionsapplied to a metal substrate is a corrosion inhibiting effective amount,i.e., an amount to prevent or reduce the rate of corrosion of the metalsubstrate. The corrosion inhibiting effective amount may vary dependingupon the use intended, and can be determined by one of ordinary skill inthe art.

Without wishing to be bound by any particular theory, it is believedthat in aqueous solutions, the quaternary ammonium salts containingnon-halogen anions described herein have a natural affinity for themetal, since they also act as cationic surfactants, and thereforemigrate to the surface of the metal. Once at the surface, the quaternaryammonium salt containing non-halogen anions block oxygen and/or air fromcausing further oxidation of the metal surface.

Typically, the corrosion inhibiting composition can be supplied ineither a dilutible concentrated form, or in a ready to use form.Generally, the ready to use form contains from about 0.005% to about1.00% by weight of quaternary ammonium salt containing non-halogenanions (such as, for example, quaternary ammonium carbonate,bicarbonate, or a mixture thereof), based upon 100% by weight of thetotal composition. Preferably, the ready to use form contains from about100 ppm to about 1000 ppm of quaternary ammonium salt containingnon-halogen anions (such as, for example, quaternary ammonium carbonate,bicarbonate, or a mixture thereof), based upon the 100% by weight oftotal composition. Preferably, the final use dilution contains fromabout 100 ppm to about 500 ppm of quaternary ammonium salt containingnon-halogen anions (such as, for example, quaternary ammonium carbonate,bicarbonate, or a mixture thereof), based upon 100% by weight of totaluse dilution.

The composition may be applied to the metal substrate by any means knownin the art, including, but not limited to, coating, depositing, dipping,soaking, brushing, spraying, mopping, washing or the like.

In preferred embodiments, the metal substrate is selected from the groupconsisting of steel, cast iron, aluminum, metal alloys, and combinationsthereof.

Coatings

The aforementioned anti-corrosive quaternary ammonium salts containing anon-halogen anion (such as, for example, the anti-corrosive quaternaryammonium carbonates, bicarbonates, and mixtures thereof), may beincorporated into anti-corrosive coatings for metal substrates. Thecoatings of the present invention include a coating material.Preferably, the quaternary ammonium salt containing non-halogen anionsis dissolved or dispersed in the coating material.

Suitable coating materials include, but are not limited to, organicresins, such as epoxy resins, urethane resins, vinyl resins, butyralresins, phthalic acid resins, curable resins, such as isocyanate andbutadiene resins, as well as traditional coatings, such as varnishes,low VOC solvent coatings based on polyurethanes, and water-basedcoatings such as rosin fatty acid vinylic emulsions. The coating may beformed by methods known in the art.

The coatings of the present invention may be, for example, paints,primers, and industrial coatings.

Additional ingredients that may be present in the coating include, butare not limited to, UV stabilizers, curing agents, hardening agents,flame retardants, and mixtures thereof.

According to one preferred embodiment, the anti-corrosive coating for ametal substrate comprises

-   -   (a) at least one quaternary ammonium salt of the formula

-   -   wherein R¹ is an optionally aryl-substituted C₁₋₂₀ alkyl group,        and R² is an optionally aryl-substituted C₁₋₂₀ alkyl group, R³        and R⁴ independently of each other are C₁₋₄ alkyl groups, X^(n−)        is an anion selected from the group consisting of hydroxide,        carbonate, bicarbonate, phosphates, phosphites, hypophosphite,        nitrate, sulfates, borates, anions of saturated and unsaturated        acyclic C₁₋₂₀ monocarboxylic acids, anions of saturated and        unsaturated C₂₋₂₀ dicarboxylic acids, and anions of        hydroxy-substituted carboxylic acids, and n denotes the        appropriate number of negative charges of said anion, and    -   (b) a coating material.

According to one embodiment, the quaternary ammonium salt(s) have theformula above with the proviso that, if both R³ and R⁴ are methyl,X^(n−) is neither carbonate nor bicarbonate.

The preferred meanings of the substituents R¹ through R⁴ described aboveapply to the anti-corrosive coating in an analogous way.

According to another preferred embodiment, the quaternary ammonium saltis one of the aforementioned anti-corrosive quaternary ammoniumcarbonates, bicarbonates, or a mixture thereof.

Preferably, the quaternary ammonium salt is dissolved or dispersed inthe coating material.

A metal substrate having the above described anti-corrosive coating onat least one surface is also an object of the present invention.

Aqueous and Non-Aqueous Solutions (Including Cleaning Solutions andMetalworking Fluids)

The aforementioned corrosion inhibitor compositions are particularlyuseful as components of aqueous cleaning solutions to retard andminimize the corrosion of metal parts, particularly steel, being cleanedwith these solutions. They are also useful as components of aqueous ornon-aqueous metalworking fluids and as components of aqueous ornon-aqueous solutions used as corrosion inhibitors in powder metallurgy.In these applications, the same preferred structures (I), (II) and (III)and the same preferred meanings of the substituents therein as specifiedabove for the quaternary ammonium salts used in the method forinhibiting corrosion and the anti-corrosive coating apply likewise. Thecorrosion inhibitor compositions also afford anti-microbial protectionto the substrate, such as metal, to which they are applied. For thepurpose of the present invention, the term “cleaning solution” refers toan aqueous acidic or alkaline solution that is employed in the cleaningof metal surfaces, e.g., the internal metal surfaces of processequipment. These cleaning solutions typically have a pH in the range ofabout 1 to about 10. Exemplary cleaning solutions and their uses aredisclosed in several patents, e.g., U.S. Pat. Nos. 3,413,160; 4,637,899;Re. 30,796; and Re. 30,714.

Cleaning solution compositions in accord with the present invention mayinclude at least one organic acid selected from the group consisting ofalkylene polyamine polycarboxylic acids, hydroxyacetic acid, formicacid, citric acid and mixtures or salts thereof together with acorrosion inhibitor in accord with the foregoing compositions present inan amount effective to inhibit the corrosion of metals in contact withthe solution. Exemplary organic acids includeN,N,N′,N′-ethylenediaminetetraacetic acid (EDTA), tetraammonium EDTA,diammonium EDTA, N-(2-hydroxyethyl)-N,N′,N′-ethylenediaminetriaceticacid (HEDTA) and salts thereof. These aqueous cleaning solutionstypically exhibit a pH from about 1 to about 10. Exemplary amounts ofcorrosion inhibitor (i.e., quaternary ammonium salt containing anon-halogen anion) are from about 0.05 to about 1 percent by weight.Exemplary organic acid cleaning solutions include those described inU.S. Pat. No. 6,521,028.

The corrosion inhibitor compositions of the present invention may alsobe used in aqueous cleaning solutions to inhibit the corrosion of metalby hypochlorite as well as by inorganic acids, e.g., sulfueric acid orphosphoric acid. These cleaning solutions include an amount of corrosioninhibitor in accord with the present invention that is sufficient toinhibit the corrosion of metals by these inorganic acids. Exemplaryamounts of corrosion inhibitor are from about 0.05 to about 1 percent byweight.

Corrosion inhibitors in accord with the present invention prevent, or atleast minimize, excess corrosion of clean base metal during chemicalcleaning operations. The corrosion inhibitor compositions may beemployed advantageously over a wide pH range in a wide number ofcleaning solutions employing an organic acid as the cleaning agent.

Cleaning solutions are frequently employed in the removal of scale andrust from ferrous metals. However, the solutions often contact othermetals that are present as an integral part of the system being cleaned.Examples of those metals include copper, copper alloys, zinc, zincalloys and the like.

The corrosion inhibitor compositions of the present inventionadvantageously are employed in an amount sufficient to inhibitacid-induced corrosion of metals that are in contact or contacted withaqueous cleaning solutions. According to one embodiment, the corrosioninhibitor compositions of the present invention are employed in anamount sufficient to give a corrosion rate less than or equal to about73.2 g·m⁻²·d⁻¹ (0.015 lb/ft²/day). The corrosion inhibitor compositionmay be dissolved or dispersed in the cleaning solution prior tocontacting the cleaning solution and the metal to be cleaned.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a picture of cold rolled plates of steel, each in adidecyldimethylammonium chloride (DDAC) solution or adidecyldimethylammonium carbonate/bicarbonate (DDACB) solution after 90minutes at room temperature.

FIG. 2 is a picture of cold rolled plates of steel, each in adidecyldimethylammonium chloride (DDAC) solution or adidecyldimethylammonium carbonate/bicarbonate (DDACB) solution after 30days at room temperature.

FIG. 3 is a picture of cold rolled plates of steel, each in adidecyldimethylarunonium chloride (DDAC) solution or adidecyldimethylammonium carbonate/bicarbonate (DDACB) solution after 9months at room temperature. A sample of cold rolled steel in deionizedwater after 5 hours is also shown.

FIG. 4 is a picture of cold rolled plates of steel after soaking for 9months at room temperature in a didecyldimethylammonium chloridesolution or a didecyldimethylammonium carbonate/bicarbonate solution,and after soaking in deionized water for 5 hours at room temperature.

The following examples illustrate the invention, but are not limitingthereof. All parts and percentages are given by weight unless otherwisestated.

Example 1 Submerged Steel Coupon Test (Reference: NB5709-151)

Di-n-decyldimethylammonium bicarbonate/carbonate (Carboquat®) wasneutralized to a pH of about 7 using various acids, such as, sulfuricacid, acetic acid, glycolic acid, citric acid, adipic acid, boric acid,or phosphoric acid. During the neutralization carbon dioxide was bubbledoff, thus forming the di-n-decyldimethylammonium salt of the respectiveacid.

A 0.1% (1000 ppm) solution of each of the salts was made. A cold rolledsteel coupon was submerged into each of the solutions and allowed tostand overnight. After that, a visual examination was made as to whetherthe steel coupon showed signs of corrosion. Coupons submerged in eitherdeionized water alone or submerged in a 0.1% solution ofdi-n-decyl-dimethylammonium chloride were run as controls. All of thesamples showed less visible corrosion than the controls, with phosphateand glycolate samples exhibiting no corrosion at all of the steelcoupon.

Humidity Chamber Testing Results (Reference: NB5751-010)

A Corrosion Inhibition Study (Reference: NB5751-001 through 018) wasdone with the objective to prepare steel panels (S-46, purchased fromQ-Panel Lab Products, Cleveland, Ohio) with various aqueous treatmentsof Phosphoquat (di-n-decyldimethylammonium phosphates, prepared byadding the amount of 85% aqueous phosphoric acid required to obtain thespecified pH to CarboShield™ 1000, which is a 50% aqueous solution ofdi-n-decyldimethylammonium (bi)carbonate (90 mol % bicarbonate, 10 mol %carbonate)), and various related controls. A plastic tank being 27.9 cm(11″) in diameter and 27.9 cm (11″) in height was used to treat thepanels. The plastic tank was filled with 9,600 grams of test solution.10.16 cm×15.24 cm×1.59 mm (4″×6′× 1/16″) steel (S-46) panels with a holeof 6.35 mm (¼″) in diameter located 6.35 mm (¼″) from the top edge weretreated by placing a plastic pipette through the hole in the panel. Upto three panels were skewed using the same pipette. This allowed for thepanels to stand upright, with only the bottom of the panel touching thebottom of the tank. The tank was then placed in an oven which was at 70°C. for one hour. After one hour, the panels were removed from the tank,dried with a paper towel and then wrapped in a plastic wrap and labeled.The test solutions prepared can be found in the list below.

Test Solutions Deionized Water

0.1% Phosphoquat (pH=2.5) in Deionized Water0.1% Phosphoquat (pH=4.0) in Deionized Water0.1% Phosphoquat (pH=7.5) in Deionized Water

After the steel panels had been treated, they were sent to AssuredTesting Services (224 River Rd., Ridgway, Pa. 15853) to undergo humiditychamber testing using ASTM# B1735-02. The test was conducted at 80%relative humidity and 80.degree. C. The Phosphoquat samples visuallyexhibited less rust than the control samples. Importantly, it has beenfound that several of the samples according to the present invention,including Phosphoquats 2.5 and 7.5 were easier to apply and performed aswell or better than a commercial flash rust inhibitor (IsoPrep.® 225,from McDermott).

Example 2

The object of this experiment was to test the removal of greasy soilwith engine cleaner formulations. A mixture of 7.5 g vegetable oil(Crisco® oil, The J. M. Smucker Co., Orville, Ohio) and 0.1 g carbonblack was heated until liquefied. 0.5 g of the heated mixture was spreadonto a metal coupon (steel coupon of 0.813×25.4×76.2 mm³ (0.032″×1″×3″)dimensions available from Q-Panel Lab Products, Cleveland Ohio) andallowed to dry. The metal coupon was then partially submerged in 50 mlof a formulation containing morpholine or didecyldimethylammoniumcarbonate/bicarbonate (DDACB), as detailed in Table 1 below. After 1hour, the metal coupon was removed from the formulation, and rinsed withwater. A visual assessment was performed as to how much of the greasysoil was removed from the submerged portion of the metal coupon. Theresults are set forth in Table 1.

As shown in Table 1, replacement of morpholine bydidecyldimethylammonium carbonate in the microemulsion results insignificant improvement in both formulation stability and cleaningability. Formulations A and B, both containing didecyldimethylammoniumcarbonate, resulted in removal of 100% of the greasy soil from the metalcoupon, and maintained one phase, whereas formulations C and D, both ofwhich contained morpholine and no didecyldimethylammonium carbonate,resulted in only 20% greasy soil removal and phase separated into twoopaque phases.

TABLE 1 Formula- Formula- Formula- Formula- tion A tion B tion C tion DIngredient (% wt/wt) (% wt/wt) (% wt/wt) (% wt/wt) Aromatic 200 ™ 6.06.0 6.0 6.0 Exxate ® 700 6.0 6.0 6.0 6.0 Dowanol ® DpnB 20.0 20.0 20.020.0 DDACB (50%) 12.0 15.0 — — Neodol ® 91-6 — — 7.5 7.5 Morpholine — —— 7.5 Deionized Water 56.0 53.0 60.5 53.0 TOTAL 100.0 100.0 100.0 100.0Appearance One phase One phase Two phases Two phases Slightly ClearOpaque Opaque hazy Greasy Soil 100% 100% 20% 20% Removal

Aromatic 200™ is a mixture of aromatic hydrocarbons available fromExxonMobil Chemical of Houston, Tex.

Exxate® 700 is oxo-heptyl acetate available from ExxonMobil Chemical ofHouston, Tex. Dowanol® DpnB is dipropylene glycol n-butyl etheravailable from Dow Chemical of Midland, Mich.

Neodol® 91-6 is a mixture of ethoxylated C₉₋₁₁ alcohols with an averagedegree of ethoxylation of six (6 moles ethylene oxide per mole ofalcohol) available from Shell Chemicals of Houston, Tex.

Example 3

Cold rolled steel coupons (mild steel coupons of 0.813×25.4×76.2 mm³(0.032″×1″×3″) dimensions (Q-Panel Lab Products, Cleveland Ohio)) werefully submerged in either deionized water or tap water, and in eitherdeionized water containing 100 or 1000 ppm of didecyldimethylammoniumcarbonate/bicarbonate (DDACB) mixture or tap water containing 100 or1000 ppm of didecyldimethylammonium carbonate/bicarbonate mixture in 120ml (4 oz.) glass jars with screw-on caps. Each solution was tested withtwo coupons (coupons 1-10 and A-J, respectively). After one week, thecoupons were removed, rinsed with either deionized or tap water andbrushed lightly with a soft nylon brush. The coupons were then driedunder a stream of nitrogen and weighed. The results are set forth inTable 2 below. Differences in weight are expressed as (−) for weightloss, or (+) for weight gain. All weight differences are given inpercent, based on the original weight of the respective coupon.

TABLE 2 Wt. [g] Wt. [g] % Wt. Sample Coupon pH (before) (after) changeDI water 1 8.6 12.6248 12.6193 −0.044 A 12.6521 12.6463 −0.046 DIwater + 100 ppm 2 9.1 12.6161 12.6112 −0.039 DDACB B 12.5611 12.5555−0.045 DI water + 1000 ppm 3 8.3 12.5870 12.5873 +0.002 DDACB C 12.582412.5824 ±0.000 DI water + 100 ppm 4 9.1 12.7384 12.7385 +0.001 DDACB D12.6235 12.6185 −0.040 DI water + 1000 ppm 5 8.9 12.7594 12.7596 +0.002DDACB E 12.6350 12.6351 +0.001 Tap water 6 7.1 12.6807 12.6735 −0.057 F12.5739 12.5667 −0.057 Tap water + 100 ppm 7 7.2 12.7034 12.6969 −0.051DDACB G 12.5835 12.5770 −0.052 Tap water + 1000 ppm 8 7.5 12.656112.6564 +0.002 DDACB H 12.5933 12.5935 +0.002 Tap water + 100 ppm 9 7.312.6553 12.6476 −0.061 DDACB I 12.6930 12.6868 −0.049 Tap water + 1000ppm 10  7.4 12.6675 12.6674 −0.001 DDACB J 12.5273 12.5284 +0.009

As shown in Table 2, solutions containing 1000 ppm ofdidecyldimethylammonium carbonate/bicarbonate did not degrade after 1week, as evidenced by essentially no loss in weight of the metal coupon.No sediment formation was observed for these samples. The other testsolutions became brown and showed sediment on the bottom of the glassjar. Corrosion was observed on the cold rolled steel coupon exposed todeionized water after one hour, while no corrosion was observed on thecoupon exposed to deionized water containing 1000 ppm of thedidecyldimethylammonium carbonate/bicarbonate after one week.

Example 4

Deionized water (58.2% w/w), surfactant (octyldimethylamine oxide (40%active), FMB-A08®, Lonza, Inc., Fair Lawn, N.J.) (8.0% w/w) and a 50%aqueous solution of a quaternary compound (didecyldimethylammoniumchloride (DDAC), or didecyldimethylammonium carbonate/bicarbonatemixture (DDACB)) (33.8% w/w) were mixed together.

A 1:256 dilution of the mixture (660 ppm active quaternary ammoniumcompound) in water was used to assess the corrosion inhibitionproperties of DDAC and DDACB. Cold rolled steel plates (steel coupons of0.813×25.4×76.2 mm³ (0.032″×1″×3″) dimensions (Q-Panel Lab Products,Cleveland Ohio)) were immersed in each of the aqueous solutions andmonitored, at room temperature, for a period of nine months.

FIGS. 1 and 2 are pictures of the plates after standing at roomtemperature in the aqueous solutions for 90 minutes and 30 days,respectively. As can be seen, the plate in the DDAC solution has startedto corrode, after only 90 minutes, and is badly corroded after 30 days.In contrast, the plate in DDACB shows no corrosion whatsoever, evenafter 30 days.

FIGS. 3 and 4 are pictures of the plates after standing at roomtemperature in the aqueous solutions for a total of 9 months. As can beseen, the plate in the DDACB solution shows no corrosion, whilst theplate in the DDAC solution is fully corroded. For comparison purposes, apiece of identical cold rolled steel, soaked in deionized (DI) watercontaining no quaternary ammonium compound is also shown. Even afteronly 5 hours in DI water, the plate shows some signs of corrosion.

All patents and publications cited herein are incorporated by referencein their entirety to the same extent as if each was individuallyincorporated by reference.

We claim:
 1. A method for inhibiting corrosion of a metal substratecomprising the step of contacting the substrate with a compositioncomprising: (a) a quaternary ammonium carbonate of formula

wherein R¹ is an optionally aryl-substituted C₁₋₂₀ alkyl group, and R²is an optionally aryl-substituted C₁₋₂₀ alkyl group, and, optionally, aquaternary ammonium bicarbonate of formula

wherein R¹ and R² are as defined above; and (b) optionally, a solvent.2. The method of claim 1, wherein R¹ and R² are the same C₁₋₂₀ alkylgroups.
 3. The method of claim 2, wherein R¹ and R² are C₁₀ alkylgroups.
 4. The method of claim 3, wherein R¹ and R² are n-C₁₀ alkylgroups.
 5. The method of claim 1, wherein R¹ is methyl.
 6. The method ofclaim 5, wherein R¹ and R² are methyl.
 7. The method of claim 1, whereinR¹ is benzyl or phenylethyl.
 8. The method claim 1, wherein thecomposition further comprises a surfactant selected from the groupconsisting of amine oxides, linear alcohol ethoxylates, secondaryalcohol ethoxylates, ethoxylate ethers, betaines, fatty acids containingfrom 6 to 22 carbon atoms, salts of fatty acids containing from 6 to 22carbon atoms, and mixtures thereof.
 9. The method of claim 8, whereinthe surfactant is nonylphenol ethoxylate.
 10. The method of claim 1,wherein the metal substrate is in an oil environment.
 11. The method ofclaim 10, wherein oil environment comprises a petroleum distillate. 12.The method of claim 11, wherein the petroleum distillate is selectedfrom the group consisting of kerosene, white spirit, hydrocarbonfractions, and mixtures thereof.
 13. The method of claim 1, wherein thecomposition further comprises at least one ingredient selected from thegroup consisting of builders, colorants, perfumes and fragrances. 14.The method of claim 1, wherein the metal substrate is selected from thegroup consisting of steel, cast iron, aluminum, metal alloys andcombinations thereof.
 15. The method of claim 1, wherein the solvent isa polar solvent selected from the group consisting of water,water-miscible polar solvents, and mixtures thereof.
 16. The method ofclaim 15, wherein the composition is an anti-corrosive cleaning solutionand the metal substrate is being cleaned with said solution.
 17. Themethod of claim 1, wherein the composition is an anti-corrosivemetalworking fluid, and wherein the metal substrate is a metal to beworked and the solvent is water or a water-oil mixture.
 18. The methodof claim 15, wherein the metal substrate is a metal powder in a powdermetallurgy process.
 19. A method for anti-corrosive cleaning of a metalsubstrate comprising the step of contacting the metal substrate with acomposition comprising: (a) at least one quaternary ammonium compoundselected from the group consisting of quaternary ammonium carbonates,quaternary ammonium bicarbonates, and mixtures thereof; and (b) asolvent.
 20. A method for metalworking using an anti-corrosive fluidcomprising the step of contacting the metal being worked with acomposition comprising: (a) at least one quaternary ammonium compoundselected from the group consisting of quaternary ammonium carbonates,quaternary ammonium bicarbonates, and mixtures thereof; and (b) asolvent.
 21. A method for inhibiting corrosion in a powder metallurgyprocess comprising the step of contacting a metal powder with acomposition comprising: (a) at least one quaternary ammonium compoundselected from the group consisting of quaternary ammonium carbonates,quaternary ammonium bicarbonates, and mixtures thereof; and (b) asolvent.